Statistics page: the statistics database's size, and a fullness bar on the disk tiles

The server section shows the statistics database's size (with its -wal and -shm) and how many answers the query log holds, linking to the dashboard's Storage panel; the disk tiles get the same bar as the dashboard. GET /stats/server has database {path, bytes, query_log_rows}.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/web/static/assets/style.css

@@ -613,3 +613,4 @@ table.recent-queries td.oneline-cell { max-width: 40ch; white-space: nowrap; ove
 .swatch { display: inline-block; width: 10px; height: 10px; border-radius: 2px; vertical-align: -1px; }
 .swatch.db { background: var(--accent); }
 .swatch.other { background: var(--muted); opacity: 0.45; }
+.card .disk-bar { margin: 6px 0 4px; height: 8px; }